Light harvesting multichromophore compositions and methods of using the same

ABSTRACT

Light harvesting luminescent multichromophores that are configured upon excitation to transfer energy to, and amplify the emission from, an acceptor signaling chromophore in energy-receiving proximity therewith are provided. Also provided are compositions for labelling a target. The labelling composition may include a donor light harvesting multichromophore and an acceptor signaling chromophore in energy-receiving proximity to the donor light harvesting multichromophore. Also provided is an aqueous composition for labelling a target, including: a donor light harvesting multichromophore; an acceptor signaling chromophore in energy-receiving proximity therewith; and a sensor biomolecule. Methods for using the subject compositions are also provided.

CROSS-REFERENCING

This patent application is a continuation of U.S. application Ser. No. 15/163,525, filed on May 24, 2016, which is a continuation of U.S. application Ser. No. 14/624,466, filed on Feb. 17, 2015, now U.S. Pat. No. 10,001,475, which is a continuation-in-part of U.S. application Ser. No. 13/356,500, filed on Jan. 23, 2012, now U.S. Pat. No. 9,371,559 which is a continuation of U.S. application Ser. No. 11/746,055, filed on May 8, 2007, now U.S. Pat. No. 8,101,416, which is a continuation of U.S. application Ser. No. 10/600,286, filed on Jun. 20, 2003, now U.S. Pat. No. 7,214,489, which claims the benefit of U.S. Provisional Application No. 60/406,266, filed on Aug. 26, 2002 and U.S. Provisional Application No. 60/390,524, filed on Jun. 20, 2002, which applications are incorporated herein by reference for all purposes; and this patent application is related to and claims the benefit of U.S. application Ser. No. 14/460,245, filed on Aug. 14, 2014, now U.S. Pat. No. 9,085,799, which is a continuation of U.S. application Ser. No. 14/086,532, filed on Nov. 21, 2013, now U.S. Pat. No. 8,841,072, which is a continuation of U.S. application Ser. No. 13/544,303, filed on Jul. 9, 2012, now U.S. Pat. No. 8,617,814, which is a continuation of U.S. application Ser. No. 12/632,734, filed on Dec. 7, 2009, now U.S. Pat. No. 8,227,187 which is a continuation of U.S. application Ser. No. 11/854,365, filed on Sep. 12, 2007, now U.S. Pat. No. 7,629,448, which is a divisional of U.S. application Ser. No. 10/648,945, filed on Aug. 26, 2003, now U.S. Pat. No. 7,270,956, which claims the benefit of U.S. Provisional Application No. 60/406,266, filed on Aug. 26, 2002; U.S. application Ser. No. 10/779,412, filed on Feb. 13, 2004, now U.S. Pat. No. 8,993,335, which claims the benefit of U.S. Provisional Application No. 60/447,860, filed on Feb. 13, 2003; and U.S. application Ser. No. 13/075,172, filed on Mar. 29, 2011, now U.S. Pat. No. 9,159,465, which is a continuation of U.S. application Ser. No. 11/561,893, filed on Nov. 21, 2006, now U.S. Pat. No. 7,914,984, which is a divisional of U.S. application Ser. No. 10/666,333, filed on Sep. 17, 2003, now U.S. Pat. No. 7,144,950; which applications are incorporated herein by reference for all purposes.

GOVERNMENT SUPPORT

The following invention was made with support from grant number DMR-0097611, awarded by the National Science Foundation. The government has certain rights in the invention.

INTRODUCTION

Dyes which, when irradiated with light of a wavelength absorbed by these substances, emit light of a (usually) different wavelength are referred to as fluorescent dyes. Fluorescent dyes find us in a variety of applications in biochemistry, biology and medicine, e.g. in diagnostic kits, in microscopy or in drug screening. Fluorescent dyes are characterized by a number of parameters allowing a user to select a suitable dye depending on the desired purpose. This includes the excitation wavelength maximum, the emission wavelength maximum, the Stokes shift, the extinction coefficient .epsilon, the fluorescence quantum yield, and the fluorescence lifetime. Dyes may be selected according to the application of interest to, e.g., allow penetration of exciting radiation into biological, to minimize background fluorescence and to achieve a high signal-to-noise ratio.

Molecular recognition involves the specific binding of two molecules. Molecules which have binding specificity for a target biomolecule find use in a variety of research and diagnostic applications, such as the labelling and separation of analytes, flow cytometry, in situ hybridization, enzyme-linked immunosorbent assays (ELISAs), western blot analysis, magnetic cell separations and chromatography. Target biomolecules may be detected by labelling with a dye.

SUMMARY

Light harvesting luminescent multichromophores that are configured upon excitation to transfer energy to, and amplify the emission from, an acceptor signaling chromophore in energy-receiving proximity therewith are provided. Also provided are compositions for labelling a target. The labelling composition may include a donor light harvesting multichromophore and an acceptor signaling chromophore in energy-receiving proximity to the donor light harvesting multichromophore. Also provided is an aqueous composition for labelling a target, including: a donor light harvesting multichromophore; an acceptor signaling chromophore in energy-receiving proximity therewith; and a sensor biomolecule. Methods for using the subject compositions to detect a target are also provided.

BRIEF DESCRIPTION OF THE FIGURES

It is understood that the drawings, described below, are for illustration purposes only. The drawings are not intended to limit the scope of the present teachings in any way.

FIG. 1 presents the emission spectra of a composition including a signaling chromophore (e.g. PNA-C*) that is either connected to conjugated polymer 1 (e.g., via binding of complementary DNA to PNA-C*) or not connected to polymer 1 (e.g., when non-complementary DNA fails to bind to PNA-C*), by excitation of polymer 1. PNA-C* and the respective DNA were added together in water at pH=5.5. The spectra are normalized with respect to the emission of polymer 1.

FIG. 2. Comparison of the intensity of signaling chromophore (e.g., EB (EB=Ethidium bromide)) emission from various compositions where a conjugated polymer and a signaling chromophore are connected via a biomolecule, e.g., polymer/ds-DNA/EB in 50 mmol phosphate buffer (pH=7.4) with [ds-DNA]=1.0 E⁻⁸ M, [Polymer RU]=2.0 E⁻⁷ M, [EB]=1.1 E⁻⁶ M. Emission intensity was normalized relative to the E value at the excitation wavelength.

DEFINITIONS

Before the present invention is described in further detail, it is to be understood that this invention is not limited to the particular methodology, devices, solutions or apparatuses described, as such methods, devices, solutions or apparatuses can, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to limit the scope of the present invention.

Use of the singular forms “a,” “an,” and “the” include plural references unless the context clearly dictates otherwise. Thus, for example, reference to “a target polynucleotide” includes a plurality of target polynucleotides, reference to “a signaling chromophore” includes a plurality of such chromophores, reference “a sensor PNA” includes a plurality of sensor PNAs, and the like. Additionally, use of specific plural references, such as “two,” “three,” etc., read on larger numbers of the same subject unless the context clearly dictates otherwise.

Terms such as “connected,” “attached,” “linked” and conjugated are used interchangeably herein and encompass direct as well as indirect connection, attachment, linkage or conjugation unless the context clearly dictates otherwise.

Where a range of values is recited, it is to be understood that each intervening integer value, and each fraction thereof, between the recited upper and lower limits of that range is also specifically disclosed, along with each subrange between such values. The upper and lower limits of any range can independently be included in or excluded from the range, and each range where either, neither or both limits are included is also encompassed within the invention. Where a value being discussed has inherent limits, for example where a component can be present at a concentration of from 0 to 100%, or where the pH of an aqueous solution can range from 1 to 14, those inherent limits are specifically disclosed. Where a value is explicitly recited, it is to be understood that values which are about the same quantity or amount as the recited value are also within the scope of the invention, as are ranges based thereon. Where a combination is disclosed, each subcombination of the elements of that combination is also specifically disclosed and is within the scope of the invention.

Conversely, where different elements or groups of elements are disclosed, combinations thereof are also disclosed. Where any element of an invention is disclosed as having a plurality of alternatives, examples of that invention in which each alternative is excluded singly or in any combination with the other alternatives are also hereby disclosed; more than one element of an invention can have such exclusions, and all combinations of elements having such exclusions are hereby disclosed.

Unless defined otherwise or the context clearly dictates otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the invention, the preferred methods and materials are now described.

All publications mentioned herein are hereby incorporated by reference for the purpose of disclosing and describing the particular materials and methodologies for which the reference was cited. The publications discussed herein are provided solely for their disclosure prior to the filing date of the present application. Nothing herein is to be construed as an admission that the invention is not entitled to antedate such disclosure by virtue of prior invention.

In describing the present invention, the following terms will be employed, and are intended to be defined as indicated below.

The terms “polynucleotide,” “oligonucleotide,” “nucleic acid” and “nucleic acid molecule” are used interchangeably herein to refer to a polymeric form of nucleotides of any length, and may comprise ribonucleotides, deoxyribonucleotides, analogs thereof, or mixtures thereof. These terms refer only to the primary structure of the molecule. Thus, the terms include triple-, double- and single-stranded deoxyribonucleic acid (“DNA”), as well as triple-, double- and single-stranded ribonucleic acid (“RNA”). It also includes modified, for example by alkylation and/or by capping, and unmodified forms of the polynucleotide. “Complementary” or “substantially complementary” refers to the ability of a first specific binding member to specifically bind to a second specific binding member (e.g., hybridize or base pair between nucleotides or nucleic acids, such as, for instance, between a sensor peptide nucleic acid and a target polynucleotide). Complementary nucleotides are, generally, A and T (or A and U), or C and G. Two single-stranded polynucleotides or PNAs are said to be substantially complementary when the bases of one strand, optimally aligned and compared and with appropriate insertions or deletions, pair with at least about 80% of the bases of the other strand, usually at least about 90% to 95% and more preferably from about 98 to 100%.

Alternatively, substantial complementarity exists when a polynucleotide or PNA will hybridize under selective hybridization conditions to its complement. Typically, selective hybridization will occur when there is at least about 65% complementary over a stretch of at least 14 to 25 bases, preferably at least about 75%, more preferably at least about 90% complementary. See, M. Kanehisa Nucleic Acids Res. 12:203 (1984).

“Preferential binding” or “preferential hybridization” refers to the increased propensity of one specific binding member (e.g., a polynucleotide or PNA) to bind to its complementary specific binding member in a sample as compared to another noncomplementary component in the sample.

“Polypeptide” and “protein” are used interchangeably herein and include a molecular chain of amino acids linked through peptide bonds. The terms do not refer to a specific length of the product. Thus, “peptides,” “oligopeptides,” and “proteins” are included within the definition of polypeptide. The terms include polypeptides containing modifications of the polypeptide, for example, glycosylations, acetylations, phosphorylations, and sulphations. In addition, protein fragments, analogs (including amino acids not encoded by the genetic code, e.g. homocysteine, ornithine, D-amino acids, and creatine), natural or artificial mutants or variants or combinations thereof, fusion proteins, and proteins comprising derivatized residues (e.g. alkylation of amine groups, acetylations or others esterifications of carboxyl groups) and the like are included within the meaning of polypeptide.

“Multiplexing” herein refers to an assay or other analytical method in which multiple analytes can be assayed simultaneously.

“Optional” or “optionally” means that the subsequently described event or circumstance may or may not occur, and that the description includes instances where the event or circumstance occurs singly or multiply and instances in which it does not occur at all. For example, the phrase “optionally substituted alkyl” means an alkyl moiety that may or may not be substituted and the description includes both unsubstituted, monosubstituted, and polysubstituted alkyls.

“Alkyl” refers to a branched, unbranched or cyclic saturated hydrocarbon group of 1 to 24 carbon atoms optionally substituted at one or more positions, and includes polycyclic compounds. Examples of alkyl groups include optionally substituted methyl, ethyl, n-propyl, isopropyl, n-butyl, s-butyl, t-butyl, n-pentyl, isopentyl, neopentyl, n-hexyl, n-heptyl, n-octyl, n-decyl, hexyloctyl, tetradecyl, hexadecyl, eicosyl, tetracosyl and the like, as well as cycloalkyl groups such as cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, adamantyl, and norbornyl. The term “lower alkyl” refers to an alkyl group of 1 to 6 carbon atoms, preferably 1 to 4 carbon atoms. Exemplary substituents on substituted alkyl groups include hydroxyl, cyano, alkoxy, ═O, ═S, —NO₂, halogen, haloalkyl, heteroalkyl, carboxyalkyl, amine, amide, thioether and —SH.

“Alkoxy” refers to an “—Oalkyl” group, where alkyl is as defined above. A “lower alkoxy” group intends an alkoxy group containing one to six, more preferably one to four, carbon atoms.

“Alkenyl” refers to a branched, unbranched or cyclic hydrocarbon group of 2 to 24 carbon atoms containing at least one carbon-carbon double bond optionally substituted at one or more positions. Examples of alkenyl groups include ethenyl, 1-propenyl, 2-propenyl (allyl), 1-methylvinyl, cyclopropenyl, 1-butenyl, 2-butenyl, isobutenyl, 1,4-butadienyl, cyclobutenyl, 1-methylbut-2-enyl, 2-methylbut-2-en-4-yl, prenyl, pent-1-enyl, pent-3-enyl, 1,1-dimethylallyl, cyclopentenyl, hex-2-enyl, 1-methyl-1-ethylallyl, cyclohexenyl, heptenyl, cycloheptenyl, octenyl, cyclooctenyl, decenyl, tetradecenyl, hexadecenyl, eicosenyl, tetracosenyl and the like. Preferred alkenyl groups herein contain 2 to 12 carbon atoms. The term “lower alkenyl” intends an alkenyl group of 2 to 6 carbon atoms, preferably 2 to 4 carbon atoms. The term “cycloalkenyl” intends a cyclic alkenyl group of 3 to 8, preferably 5 or 6, carbon atoms. Exemplary substituents on substituted alkenyl groups include hydroxyl, cyano, alkoxy, ═O, ═S, —NO₂, halogen, haloalkyl, heteroalkyl, amine, thioether and —SH.

“Alkenyloxy” refers to an “—Oalkenyl” group, wherein alkenyl is as defined above.

“Alkylaryl” refers to an alkyl group that is covalently joined to an aryl group. Preferably, the alkyl is a lower alkyl. Exemplary alkylaryl groups include benzyl, phenethyl, phenopropyl, 1-benzylethyl, phenobutyl, 2-benzylpropyl and the like.

“Alkylaryloxy” refers to an “—Oalkylaryl” group, where alkylaryl is as defined above.

“Alkynyl” refers to a branched or unbranched hydrocarbon group of 2 to 24 carbon atoms containing at least one —C≡C— triple bond, optionally substituted at one or more positions. Examples of alkynyl groups include ethynyl, n-propynyl, isopropynyl, propargyl, but-2-ynyl, 3-methylbut-1-ynyl, octynyl, decynyl and the like. Preferred alkynyl groups herein contain 2 to 12 carbon atoms. The term “lower alkynyl” intends an alkynyl group of 2 to 6, preferably 2 to 4, carbon atoms, and one —C≡C— triple bond. Exemplary substituents on substituted alkynyl groups include hydroxyl, cyano, alkoxy, ═O, ═S, —NO2, halogen, haloalkyl, heteroalkyl, amine, thioether and —SH.

“Amide” refers to —C(O)NR′R″, where R′ and R″ are independently selected from hydrogen, alkyl, aryl, and alkylaryl.

“Amine” refers to an —N(R′)R″ group, where R′ and R″ are independently selected from hydrogen, alkyl, aryl, and alkylaryl.

“Aryl” refers to an aromatic group that has at least one ring having a conjugated pi electron system and includes carbocyclic, heterocyclic, bridged and/or polycyclic aryl groups, and can be optionally substituted at one or more positions. Typical aryl groups contain 1 to 5 aromatic rings, which may be fused and/or linked. Exemplary aryl groups include phenyl, furanyl, azolyl, thiofuranyl, pyridyl, pyrimidyl, pyrazinyl, triazinyl, biphenyl, indenyl, benzofuranyl, indolyl, naphthyl, quinolinyl, isoquinolinyl, quinazolinyl, pyridopyridinyl, pyrrolopyridinyl, purinyl, tetralinyl and the like. Exemplary substituents on optionally substituted aryl groups include alkyl, alkoxy, alkylcarboxy, alkenyl, alkenyloxy, alkenylcarboxy, aryl, aryloxy, alkylaryl, alkylaryloxy, fused saturated or unsaturated optionally substituted rings, halogen, haloalkyl, heteroalkyl, —S(O)R, sulfonyl, —SO₃R, —SR, —NO₂, —NRR′, —OH, —CN, —C(O)R, —OC(O)R, —NHC(O)R, —(CH₂)_(n)CO₂R or —(CH₂)_(n)CONRR′ where n is 0-4, and wherein R and R′ are independently H, alkyl, aryl or alkylaryl.

“Aryloxy” refers to an “—Oaryl” group, where aryl is as defined above.

“Carbocyclic” refers to an optionally substituted compound containing at least one ring and wherein all ring atoms are carbon, and can be saturated or unsaturated.

“Carbocyclic aryl” refers to an optionally substituted aryl group wherein the ring atoms are carbon.

“Halo” or “halogen” refers to fluoro, chloro, bromo or iodo. “Halide” refers to the anionic form of the halogens.

“Haloalkyl” refers to an alkyl group substituted at one or more positions with a halogen, and includes alkyl groups substituted with only one type of halogen atom as well as alkyl groups substituted with a mixture of different types of halogen atoms. Exemplary haloalkyl groups include trihalomethyl groups, for example trifluoromethyl.

“Heteroalkyl” refers to an alkyl group wherein one or more carbon atoms and associated hydrogen atom(s) are replaced by an optionally substituted heteroatom, and includes alkyl groups substituted with only one type of heteroatom as well as alkyl groups substituted with a mixture of different types of heteroatoms. Heteroatoms include oxygen, sulfur, and nitrogen. As used herein, nitrogen heteroatoms and sulfur heteroatoms include any oxidized form of nitrogen and sulfur, and any form of nitrogen having four covalent bonds including protonated forms. An optionally substituted heteroatom refers to replacement of one or more hydrogens attached to a nitrogen atom with alkyl, aryl, alkylaryl or hydroxyl.

“Heterocyclic” refers to a compound containing at least one saturated or unsaturated ring having at least one heteroatom and optionally substituted at one or more positions. Typical heterocyclic groups contain 1 to 5 rings, which may be fused and/or linked, where the rings each contain five or six atoms. Examples of heterocyclic groups include piperidinyl, morpholinyl and pyrrolidinyl. Exemplary substituents for optionally substituted heterocyclic groups are as for alkyl and aryl at ring carbons and as for heteroalkyl at heteroatoms.

“Heterocyclic aryl” refers to an aryl group having at least 1 heteroatom in at least one aromatic ring. Exemplary heterocyclic aryl groups include furanyl, thienyl, pyridyl, pyridazinyl, pyrrolyl, N-lower alkyl-pyrrolo, pyrimidyl, pyrazinyl, triazinyl, tetrazinyl, triazolyl, tetrazolyl, imidazolyl, bipyridyl, tripyridyl, tetrapyridyl, phenazinyl, phenanthrolinyl, purinyl and the like.

“Hydrocarbyl” refers to hydrocarbyl substituents containing 1 to about 20 carbon atoms, including branched, unbranched and cyclic species as well as saturated and unsaturated species, for example alkyl groups, alkylidenyl groups, alkenyl groups, alkylaryl groups, aryl groups, and the like. The term “lower hydrocarbyl” intends a hydrocarbyl group of one to six carbon atoms, preferably one to four carbon atoms.

A “substituent” refers to a group that replaces one or more hydrogens attached to a carbon or nitrogen. Exemplary substituents include alkyl, alkylidenyl, alkylcarboxy, alkoxy, alkenyl, alkenylcarboxy, alkenyloxy, aryl, aryloxy, alkylaryl, alkylaryloxy, —OH, amide, carboxamide, carboxy, sulfonyl, ═O, ═S, —NO₂, halogen, haloalkyl, fused saturated or unsaturated optionally substituted rings, —S(O)R, —SO₃R, —SR, —NRR′, —OH, —CN, —C(O)R, —OC(O)R, —NHC(O)R, —(CH₂)_(n)CO₂R or —(CH₂)_(n)CONRR′ where n is 0-4, and wherein R and R′ are independently H, alkyl, aryl or alkylaryl. Substituents also include replacement of a carbon atom and one or more associated hydrogen atoms with an optionally substituted heteroatom.

“Sulfonyl” refers to —S(O)₂R, where R is alkyl, aryl, —C(CN)═C-aryl, —CH2CN, alkylaryl, or amine.

“Thioamide” refers to —C(S)NR′R″, where R′ and R″ are independently selected from hydrogen, alkyl, aryl, and alkylaryl.

“Thioether” refers to —SR, where R is alkyl, aryl, or alkylaryl.

The term “antibody” as used herein includes antibodies obtained from both polyclonal and monoclonal preparations, as well as: hybrid (chimeric) antibody molecules (see, for example, Winter et al. (1991) Nature 349:293-299; and U.S. Pat. No. 4,816,567); F(ab′)2 and F(ab) fragments; Fv molecules (noncovalent heterodimers, see, for example, Inbar et al. (1972) Proc Natl Acad Sci USA 69:2659-2662; and Ehrlich et al. (1980) Biochem 19:4091-4096); single-chain Fv molecules (sFv) (see, for example, Huston et al. (1988) Proc Natl Acad Sci USA 85:5879-5883); dimeric and trimeric antibody fragment constructs; minibodies (see, e.g., Pack et al. (1992) Biochem 31:1579-1584; Cumber et al. (1992) J Immunology 1496:120-126); humanized antibody molecules (see, for example, Riechmann et al. (1988) Nature 332:323-327; Verhoeyan et al. (1988) Science 239:1534-1536; and U.K. Patent Publication No. GB 2,276,169, published 21 Sep. 1994); and, any functional fragments obtained from such molecules, wherein such fragments retain specific-binding properties of the parent antibody molecule.

As used herein, the term “monoclonal antibody” refers to an antibody composition having a homogeneous antibody population. The term is not limited regarding the species or source of the antibody, nor is it intended to be limited by the manner in which it is made. Thus, the term encompasses antibodies obtained from murine hybridomas, as well as human monoclonal antibodies obtained using human hybridomas or from murine hybridomas made from mice expression human immunoglobulin chain genes or portions thereof. See, e.g., Cote, et al. Monoclonal Antibodies and Cancer Therapy, Alan R. Liss, 1985, p. 77.

DETAILED DESCRIPTION

As summarized above, compositions including luminescent light harvesting multichromophores that are configured upon excitation to transfer energy to, and amplify the emission from, an acceptor signaling chromophore in energy-receiving proximity therewith are provided. The light harvesting multichromophores find use in a variety of applications, including analyte detection applications.

Light Harvesting, Luminescent Multichromophore Systems

Luminescent light harvesting multichromophore systems are efficient light absorbers by virtue of the multiple chromophores they include. Light harvesting multichromophores of interest include, but are not limited to, conjugated polymers, aggregates of conjugated molecules, luminescent dyes attached via side chains to saturated polymers, semiconductor quantum dots and dendritic structures. In some instances, the light harvesting multichromophore system includes a light harvesting conjugated polymer. For example, each repeat unit on a conjugated polymer can be considered as a contributing chromophore, quantum dots are made up of many atoms, a saturated polymer can be functionalized with many luminescent dye molecules on side chains, and dendrimers can be synthesized containing many covalently bonded individual chromophores. Attachment of chromophore assemblies onto solid supports, such as polymer beads or surfaces, can also be used for light harvesting.

In some instances, the water soluble, light harvesting multichromophore has a luminescent emission spectrum, i.e., the multichromophore is itself luminescent. In some cases, water soluble, light harvesting multichromophore has high luminescence quantum efficiency. In certain cases, the water soluble, light harvesting multichromophore has high fluorescent efficiency. Light harvesting multichromophore systems can also efficiently transfer energy to nearby luminescent species (e.g., “signaling chromophores”). Mechanisms for energy transfer include, for example, resonant energy transfer (Förster (or fluorescence) resonance energy transfer, FRET), quantum charge exchange (Dexter energy transfer) and the like. In some cases, however, these energy transfer mechanisms are relatively short range; that is, close proximity of the light harvesting multichromophore system to the signaling chromophore is required for efficient energy transfer. As used herein, the term “energy receiving proximity” refers to an arrangement of the light harvesting multichromophore system and the signaling chromophore sufficient for efficient energy transfer, e.g., via FRET. Under conditions for efficient energy transfer, amplification of the emission from the signaling chromophore occurs when the number of individual chromophores in the light harvesting multichromophore system is large; that is, the emission from the signaling chromophore is more intense when the incident light (the “pump light”) is at a wavelength which is absorbed by the light harvesting multichromophore system than when the signaling chromophore is directly excited by the pump light.

When the average distance between the light harvesting multichromophore and the signaling chromophore is too large for effective energy transfer, there is little or no emission from the signaling chromophore. As such, the light harvesting multichromophore may be configured upon excitation to transfer energy to, and amplify the emission from, an acceptor signaling chromophore in energy-receiving proximity therewith.

The light harvesting multichromophore and the signaling chromophore (C*) are selected so that the absorption bands of the two chromophores have minimal overlap and so that the luminescent emission spectra of the two species are at different wavelengths. In some instances, the water soluble, light harvesting multichromophore has a luminescent emission spectrum, i.e., the multichromophore is luminescent.

As shown by Förster, dipole-dipole interactions lead to long-range resonance energy transfer (FRET) from a donor chromophore to an acceptor chromophore. The energy transfer efficiency (E) is proportional to 1/r⁶, where r is the donor-acceptor distance, and the overlap integral, as shown in Equation 1.

$\begin{matrix} {E \propto {{\frac{1}{r^{6}} \cdot \underset{0}{\overset{\infty}{\mathcal{o}}}}{F_{D}(\lambda)}{ɛ_{A}(\lambda)}\lambda^{4}d\;\lambda}} & (1) \end{matrix}$

The distance requirement for energy transfer in the compositions described herein may be controlled by the configuration of the donor and the acceptor. The overlap integral expresses the spectral overlap between the emission of the donor and the absorption of the acceptor. The components of the labelling composition and their relative configuration can be selected so that their optical properties meet this requirement.

In some instances, the light harvesting multichromophores described herein are soluble in aqueous solutions and other polar solvents, and in some cases are soluble in water, i.e., they are water-soluble. By “water-soluble” is meant that the material exhibits solubility in a predominantly aqueous solution, which, although comprising more than 50% by volume of water, does not exclude other substances from that solution, including without limitation buffers, blocking agents, co-solvents, salts, metal ions and detergents. It is understood that the light harvesting multichromophores may be selected and/or adapted to achieve a variety of desirable characteristics (such as water solubility) using any convenient methods and materials, such as the methods and materials described by N. Angelova and D. Hunkeler in “Rationalizing the design of polymeric biomaterials”, TIBTECH, October 1999, 17, 409-421; and S. Zalipsky in “Functionalized poly(ethylene glycol) for preparation of biologically relevant conjugates”, Bioconjugate Chemistry 1995, 6 (2), 150-165. In some instances, the light harvesting multichromophores include water-soluble groups which improve the water solubility of the molecules. In certain instances, the light harvesting multichromophore is conjugated to another water soluble molecule, such as a biomolecule. In certain cases, the light harvesting multichromophore is conjugated to a sensor.

Any convenient water-soluble groups (WSGs) may be utilized in the subject light harvesting multichromophores. The term “water-soluble group” refers to a functional group that is well solvated in aqueous environments and that imparts improved water solubility to the molecules to which it is attached. In some embodiments, a WSG increases the solubility of the multichromophore in a predominantly aqueous solution (e.g., as described herein), as compared to a multichromophore which lacks the WSG. The water soluble groups may be any convenient hydrophilic group that is well solvated in aqueous environments. In some cases, the hydrophilic water soluble group is charged, e.g., positively or negatively charged. In certain cases, the hydrophilic water soluble group is a neutral hydrophilic group. In some embodiments, the WSG is a hydrophilic polymer, e.g., a polyethylene glycol, a cellulose, a chitosan, or a derivative thereof.

As used herein, the terms “polyethylene oxide”, “PEO”, “polyethylene glycol” and “PEG” are used interchangeably and refer to a polymer including a chain described by the formula —(CH₂—CH₂—O—)_(n)— or a derivative thereof. In some embodiments, “n” is 5000 or less, such as 1000 or less, 500 or less, 200 or less, 100 or less, 50 or less, 40 or less, 30 or less, 20 or less, 15 or less, such as 5 to 15, or 10 to 15. It is understood that the PEG polymer may be of any convenient length and may include a variety of terminal groups, including but not limited to, alkyl, aryl, hydroxyl, amino, acyl, acyloxy, and amido terminal groups. Functionalized PEGs that may be adapted for use in the subject multichromophores include those PEGs described by S. Zalipsky in “Functionalized poly(ethylene glycol) for preparation of biologically relevant conjugates”, Bioconjugate Chemistry 1995, 6 (2), 150-165.

Water soluble groups of interest include, but are not limited to, carboxylate, phosphonate, phosphate, sulfonate, sulfate, sulfinate, ester, polyethylene glycols (PEG) and modified PEGs, hydroxyl, amine, ammonium, guanidinium, polyamine and sulfonium, polyalcohols, straight chain or cyclic saccharides, primary, secondary, tertiary, or quaternary amines and polyamines, phosphonate groups, phosphinate groups, ascorbate groups, glycols, including, polyethers, —COOM′, —SO₃M′, —PO₃M′, —NR₃ ⁺, Y′, (CH₂CH₂O)_(p)R and mixtures thereof, where Y′ can be any halogen, sulfate, sulfonate, or oxygen containing anion, p can be 1 to 500, each R can be independently H or an alkyl (such as methyl) and M′ can be a cationic counterion or hydrogen, —(CH₂CH₂O)_(yy)CH₂CH₂XR^(yy), —(CH₂CH₂O)_(yy)CH₂CH₂X—, —X(CH₂CH₂O)_(yy)CH₂CH₂—, glycol, and polyethylene glycol, wherein yy is selected from 1 to 1000, X is selected from O, S, and NR^(ZZ), and R^(ZZ) and R^(YY) are independently selected from H and C1-3 alkyl.

In some embodiments, the light harvesting multichromophore includes cationic WSGs and is polycationic. Any suitable cationic WSGs may be incorporated into the light harvesting multichromophores, including, but not limited to, ammonium groups, guanidinium groups, histidines, polyamines, pyridinium groups, and sulfonium groups.

The water solubility of light harvesting multichromophores (e.g., CPs), finds use in detecting biological targets, and in some cases is achieved by including water-soluble groups (e.g., hydrophilic groups, such as PEG or modified PEG groups or charged groups attached to the CP backbone). In some instances, the light harvesting multichromophores are conjugated polymers, which include sulfonate or carboxylate functionalities.

Exemplary multichromophores which can be used include, but are not limited to, conjugated polymers (which includes oligomers), saturated polymers or dendrimers incorporating multiple chromophores in any viable manner, and semiconductor nanocrystals (SCNCs). In some cases, the conjugated polymers, saturated polymers and dendrimers can be prepared to incorporate multiple WSGs or can be derivatized after synthesis. For example, in Example 4, Schemes 2 and 3 depict the preparation of conjugated polymers that may be adapted to include any convenient substituted alkyl (e.g., bromo-substituted alkyl) substituents. Any convenient substituents (such as water soluble groups) may be selected for inclusion in the subject conjugated polymers via polymer derivatization after polymer synthesis, e.g., via nucleophilic substitution of the bromoalkyl substitutent groups with any convenient nucleophilic groups to produce heteroalkyl substituted conjugated polymers.

In some embodiments, a water soluble light harvesting multichromophore is a conjugated polymer that includes water soluble groups. For example, water soluble conjugated molecules of interest which may be prepared according to the methods described herein include, but are not limited to, polymer 1 (where n=2-100,000), oligomer 1 and oligomer 2, shown below. In some instances, the water soluble light harvesting multichromophores have a structure selected from the formula of polymer 1, the formula of oligomer 1 or the formula of oligomer 2, depicted below. However, the specific molecular structures of polymer 1, oligomer 1 and oligomer 2, depicted below are not critical, and any water soluble light harvesting molecules can be used.

A specific example is shown in structure 1 where the water soluble conjugated polymer is poly((9,9-bis(6′-N,N,N-trimethylammonium)-hexyl)-fluorene phenylene) (denoted in the following as polymer 1). In some cases, the particular size of the subject conjugated polymers is not critical, so long as the CP is able to absorb light and transfer energy to signaling chromophores that are configured in energy receiving proximity. In some cases, values of “n” fall within the range of two to about 100,000. This specific molecular structure is not critical; any water soluble conjugated polymer with relatively high luminescence quantum efficiency can be used.

In some instances, the water soluble light harvesting multichromophore is a conjugated oligomer, such as a water soluble, cationic, luminescent conjugated oligomer, as shown below (denoted herein as oligomer 2):

In certain cases, in aqueous media, oligomers such as 2 may be more soluble than their polymeric counterparts, and hydrophobic interactions with sensor biomolecules may be less important for 2 than for larger polymer structures.

Addition of organic solvents to the subject compositions, for example a water miscible organic solvent such as ethanol, can result in a decrease in background (C*) emission. The presence of the organic solvent can decrease hydrophobic interactions between the light harvesting multichromophore and another component of the assay and thereby reduce background signal.

Conjugated Polymers

In some embodiments, the light harvesting multichromophore is a conjugated polymer. Conjugated polymers (CPs) are characterized by a delocalized electronic structure and, in some cases, can be used as highly responsive optical reporters for chemical and biological targets. In a CP, the effective conjugation length may be substantially shorter than the length of the polymer chain, and thus the backbone may contain a large number of conjugated segments in close proximity. In some instances, conjugated polymers are efficient for light harvesting and provide for optical amplification via Förster energy transfer to a signalling chromophore. In certain instances, water-soluble CPs show exceptional fluorescence quenching efficiencies in the presence of acceptor in energy-receiving proximity and are of interest for transduction of biological recognition events, among other uses.

In one embodiment, a conjugated polymer is represented by Formula A:

where:

CP₁, CP₂, CP₃, and CP₄ are optionally substituted conjugated polymer segments or oligomeric structures, and may be the same or different from one another;

LU₁ and LU₂ are each independently a linker unit;

G₁ and G are each independently a capping unit;

a, b, c, d, e and f are each independently 0 to 250; and

m and n are each independently 0 to 10,000, where m+n>1.

CP₁, CP₂, CP₃, and CP₄ may be independently aromatic repeat units, and, in some cases, may be selected from the group consisting of benzene, naphthalene, anthracene, fluorene, thiophene, furan, pyridine, and oxadiazole, each optionally substituted.

In some embodiments, the formula contains linker units LU₁ and LU₂ which may be angled linkers (e.g., as described herein) and, in some cases, can be mono- or polycyclic optionally substituted aryl groups having 5 to 20 atoms (e.g., an aromatic repeat unit of Table 1 or 2). The linker units may be evenly or randomly distributed along the polymer main chain. Aromatic rings of interest include those which also produce a spatial twist of the polymer main chain, preventing the conjugated polymer from forming a plane across that linker unit.

In some embodiments, LU₁ and LU₂ are independently selected from the group consisting of benzene derivatives incorporated into the polymer in the 1,2 or 1,3-positions; naphthalene derivatives incorporated into the polymer in the 1,2-, 1,3-, 1,6-, 1,7-, 1,8-positions; anthracene derivatives incorporated into the polymer in the 1,2-, 1,3-, 1,6-, 1,7-, 1,8-, and 1,9-positions; biphenyl derivatives incorporated into the polymer in the 2,3-, 2,4-, 2,6-, 3,3′-, 3,4-, 3,5-, 2,2′-, 2,3′-, 2,4′-, and 3,4′-positions; and corresponding heterocycles. The position numbers are given with reference to unsubstituted carbon-based rings, but the same relative positions of incorporation in the polymer are encompassed in substituted rings and/or heterocycles should their distribution of substituents change the ring numbering.

In some instances, CP₁, CP₂, CP₃, CP₄, LU₁ and LU₂ are each optionally substituted at one or more positions with one or more groups selected from —R¹-A, —R²—B, —R³—C, —R⁴-D and —R⁵—I, which may be attached through bridging functional groups -E- and —F— (see e.g., the units depicted in Tables 1 and 2). In some instances, R¹, R², R³, R⁴ and R⁵ are independently selected from alkyl, alkenyl, alkoxy, alkynyl, and aryl, alkylaryl, arylalkyl, and polyalkylene oxide, each optionally substituted, which may contain one or more heteroatoms, or may be not present. In some instances, R¹, R², R³, R⁴ and R⁵ can be independently selected from C₁₋₂₂ alkyl, C₁₋₂₂ alkoxy, C₁₋₂₂ ester, polyalkylene oxide having from 1 to about 22 carbon atoms, cyclic crown ether having from 1 to about 22 carbon atoms, or not present. In some instances, R¹, R², R³, R⁴ and R⁵ may be selected from straight or branched alkyl groups having 1 to about 12 carbon atoms, or alkoxy groups with 1 to about 12 carbon atoms. It is to be understood that more than one functional group may be appended to the rings as indicated in the formulas at one or more positions.

In some instances, A, B, C, D and I are independently selected from H, a WSG, —SiR′R″R′″, —N⁺R′R″R′″, a guanidinium group, histidine, a polyamine, a pyridinium group, and a sulfonium group. In some instances, R′, R″ and R′″ are independently selected from the group consisting of hydrogen, C₁₋₁₂ alkyl and C₁₋₁₂ alkoxy and C₃₋₁₀ cycloalkyl. In certain embodiments, R′, R″ and R′″ are lower alkyl or lower alkoxy groups. In some embodiments, E and F are independently selected from not present, —O—, —S—, —C(O)—, —C(O)O—, —C(R)(R′)—, —N(R′)—, and —Si(R′)(R″), wherein R′ and R″ are as defined above. In some embodiments, E and F are —O—. In some embodiments, E and F are not present. In some instances, A, B, C, D and I are H. In certain instances, A, B, C, D and I are independently a WSG.

In some cases, X is O, S, Se, —N(R′)— or —C(R′)(R″)—, and Y and Z are independently selected from —C(R)═ and —N═, where R, R′ and R″ are as defined above.

In certain instances, m and n are independently 0 to 10,000, wherein m+n>1. In certain embodiments, m and n are each independently 0 to 20 and in some cases from 0 to 10. Each repeat of m and n may be the same as or different than the other repeats thereof. In some embodiments, b and e are independently 0 to 250, where b+e>1. In certain cases, a, c, d and f are independently 0 to 250. In some embodiments, b and e are each 0.

Any convenient capping units may be utilized in the conjugated polymers. In some instances, G and G₁ are capping units and may be the same or different. The capping units may be activated units that allow further chemical reaction to the terminal of the polymer chain. In some cases, G and G₁ may be a group that includes a reactive functional group suitable for conjugation to a biomolecule. Any convenient activated units may be utilized as capping units G and/or G₁ in the subject CPs. The capping units may be nonactivated termination units. In certain instances, G and G₁ can be independently selected from hydrogen, optionally substituted aryl, halogen substituted aryl, boronic acid substituted aryl, and boronate radical substituted aryl.

Also provided are conjugated polymer compositions of formula A where CP₁, CP₂, CP₃, CP₄, LU₁ and LU₂ are each optionally substituted at one or more positions with one or more groups selected from —R¹-A, —R²—B, —R³—C, —R⁴-D and —R⁵—I where A, B, C, D and I are each H, which may be attached via bridging functional groups -E- and —F—. In some instances, R¹, R², R³, R⁴ and R⁵ are independently selected from alkyl, alkenyl, alkoxy, alkynyl, and aryl, alkylaryl, arylalkyl, and polyalkylene oxide, each optionally substituted, which may contain one or more heteroatoms, or may be not present. In some embodiments, E and F are independently selected from not present, —O—, —S—, —C(O)—, —C(O)O—, —C(R)(R′)—, —N(R′)—, and —Si(R′)(R″), wherein R′ and R″ are as defined above.

In certain embodiments of Formula A, at least one of —R¹-A, —R²—B, —R³—C, —R⁴-D and —R⁵—I includes a water soluble group (WSG). In some instances, R³—C and —R⁴-D each independently include a water soluble group. In certain embodiments, —R¹-A, —R²—B and —R⁵—I are each H. In certain instances, E and R⁵—I are not present. In certain embodiments, R³ and R⁴ are alkyl, each optionally substituted.

In certain embodiments the light harvesting multichromophore is a conjugated polymer including a conjugated segment having the structure:

where n, E, —R¹-A, —R²—B, —R³—C, —R⁴-D and —R⁵—I are as defined above. In certain embodiments, at least one of —R¹-A, —R²—B, —R³—C, —R⁴-D and —R⁵—I includes a water soluble group (WSG). In some instances, R³—C and —R⁴-D each independently include a water soluble group. In certain embodiments, —R¹-A, —R²—B and —R⁵—I are each H. In certain instances, E and R⁵—I are not present. In certain embodiments, R³ and R⁴ are alkyl, each optionally substituted.

Aromatic repeat units of interest are shown in Table 1 below, and representative polymeric segments and oligomeric structures are shown in Table 2.

TABLE 1 Aromatic repeat units of interest for the construction of conjugated segments and oligomeric structures.

TABLE 2 Examples of conjugated segments and oligomeric structures of CPs

Conformationally Flexible CPs

Conjugated polymers (CPs) are efficient light-gathering molecules with properties desirable for a variety of applications. Conjugated polymers can serve as light harvesting materials and signal transducers in fluorescent biosensor applications. These molecules can detect, transduce and/or amplify chemical, biological or physical information into optical and/or electrical signals. CPs can provide the advantage of collective response relative to non-interacting small molecules. This collective response influences optoelectronic properties, such as Förster resonance energy transfer (FRET), electrical conductivity and fluorescence efficiency, properties which can be used to report, or “transduce,” target analyte presence.

Aspects of the invention include conjugated polymers (CPs) including monomers which perturb the polymer's ability to form rigid-rod structures, allowing them to form a greater range of three-dimensional structures. The monomers may include aromatic molecules having attachment points to the adjacent subunits of the polymer which form an angle of greater than about 25°. The monomers may introduce a torsional twist in the conjugated polymer, thereby further disrupting the ability of the polymer to form a rigid-rod structure.

A synthetic method is also provided for producing CPs with a range of backbone regiochemistries. Such CPs exhibit facile energy transfer amongst polymer segments which results in similar emission properties and FRET function. In some instances, the flexible CPs are efficient excitation donors with respect to particular biomolecules and find use in bioassays that take advantage of the optical amplification of water-soluble conjugated polymers.

In one aspect, a plurality of CPs with different structures are provided, which may be in the form of a library. The CPs may be tested for any property of interest. For example, the CPs may be tested for increased fluorescent efficiency, for decreased self-quenching, increased Stoke's shift, and for emission wavelength.

In some embodiments, modification of polymer shape is achieved through fractional incorporation of meta and para linkages on phenylene units adjacent to fluorenyl monomer units. The meta to para ratio may be controlled during the polymerization reaction by use of, for example, 1,3-phenylenebisboronic acid and 1,4-phenylenebisboronic acid in appropriate ratios. The corresponding polymers may have ratios of meta to para linkages ranging from 0 to 100%. In some cases, the introduction of the meta linkage not only permits shape control, but also provides the possibility of energy transfer along the polymer main chain, or between different polymer segments, since fragments containing a higher fraction of para linkages may be of lower energy level, and may behave as low energy traps.

Conformationally flexible conjugated polymers (CPs) may include angled linkers with a substitution pattern (or regiochemistry) capable of perturbing the polymers' ability to form rigid-rod structures, allowing the CPs to have a greater range of three-dimensional structures. The CPs may include at least three subunits with at least one angled linker, which may be internal and/or an end unit, and may comprise at least 4, 5, 6, 8, 10, 15, 20, 25 or more subunits. The CPs may include up to about 100, 200, 300, 500, 1000, 2000, 5000, 10000, 20000, 50000 or more subunits.

The angled linker(s) are optionally substituted aromatic molecules having at least two separate bonds to other polymer components (e.g., monomers, block polymers, end groups) that are capable of forming angles relative to one another which disrupt the overall ability of the polymer to form an extended rigid-rod structure (although significant regions exhibiting such structure may remain.) The angled linkers may be bivalent or polyvalent.

The angle which the angled linkers are capable of imparting to the polymeric structure is determined as follows. Where the two bonds to other polymeric components are coplanar, the angle can be determined by extending lines representing those bonds to the point at which they intersect, and then measuring the angle between them. Where the two bonds to other polymeric components are not coplanar, the angle can be determined as follows: a first line is drawn between the two ring atoms to which the bonds attach; two bond lines are drawn, one extending from each ring atom in the direction of its respective bond to the other polymeric component to which it is joined; the angle between each bond line and the first line is fixed; and the two ring atoms are then merged into a single point by shrinking the first line to a zero length; the angle then resulting between the two bond lines is the angle the angled linker imparts to the CP.

The angle which an angled linker is capable of imparting to the polymer is in some cases less than 155°, and may be less than 150°, less than 145°, less than 140°, less than 135°, less than 130°, less than 125°, less than 120°, less than 115°, less than 110°, less than 105°, less than 100°, less than 95°, less than 90°, less than 85°, less than 80°, less than 75°, less than 70°, less than 65°, less than 60°, less than 55°, or less than 50°. The angled linker may form an angle to its adjacent polymeric units of about 25°, 30°, 35°, 40°, 45°, 50°, 60° or more. The angled linker may introduce a torsional twist in the conjugated polymer, thereby further disrupting the ability of the polymer to form a rigid-rod structure. For angled linkers having an internally rotatable bond, such as polysubstituted biphenyl, the angled linker may be capable of imparting an angle of less than about 155° in at least one orientation.

For six-membered rings, such angles can be achieved through ortho or meta linkages to the rest of the polymer. For five-membered rings, adjacent linkages fall within this range. For eight-membered rings, linkages extending from adjacent ring atoms, from alternate ring atoms (separated by one ring atom), and from ring atoms separated by two other ring atoms fall within this range. Ring systems with more than eight ring atoms may be used. For polycyclic structures, even more diverse linkage angles can be achieved.

Exemplary linking units which meet these limitations include benzene derivatives incorporated into the polymer in the 1, 2 or 1,3-positions; naphthalene derivatives incorporated into the polymer in the 1,2-, 1,3-, 1,6-, 1,7-, 1,8-positions; anthracene derivatives incorporated into the polymer in the 1,2-, 1,3-, 1,6-, 1,7-, 1,8-, and 1,9-positions; biphenyl derivatives incorporated into the polymer in the 2,3-, 2,4-, 2,6-, 3,3′-, 3,4-, 3,5-, 2,2′-, 2,3′-, 2,4′-, and 3,4′-positions; and corresponding heterocycles. The position numbers are given with reference to unsubstituted carbon-based rings, but the same relative positions of incorporation in the polymer are encompassed in substituted rings and/or heterocycles should their distribution of substituents change the ring numbering.

The CP in some cases contains at least 0.01 mol % of the angled linker, and may contain at least 0.02 mol %, at least 0.05 mol %, at least 0.1 mol %, at least 0.2 mol %, at least 0.5 mol %, at least 1 mol %, at least 2 mol %, at least 5 mol %, at least 10 mol %, at least 20 mol %, or at least 30 mol %. The CCP may contain up to 100 mol % of the angled linker, and may contain 99 mol % or less, 90 mol % or less, 80 mol % or less, 70 mol % or less, 60 mol % or less, 50 mol % or less, or 40 mol % or less.

The CP can be a copolymer, and may be a block copolymer, a graft copolymer, or both. The angled linker may be incorporated into the CP randomly, alternately, periodically and/or in blocks. In one aspect, the angled linker can be selected from aromatic or heteroaromatic structures in which the shortest link between the linking points to the polymer involves an even number of atoms bonded to one another.

In some instances, the conformationally flexible CPs are water soluble, and any or all of the subunits of the polymer may comprise one or more water soluble groups, including the angled linker(s).

Synthesis of Conjugated Polymers

A synthetic approach of interest is as follows. A neutral conjugated polymer is formed by the Suzuki coupling of a targeted ratio of monomer units, to produce a neutral conjugated polymer that may include heteroalkyl substituents. For example, as depicted in example, Schemes 2 and 3, 1,3-phenylenebisboronic acid and/or 1,4-phenylenebisboronic acid may be coupled with 2,7-dibromo-9,9-bis(6′-bromohexyl)fluorene to produce a substituted neutral CP. In some embodiments, the heteroalkyl substituted conjugated polymer may be further derivatized with any convenient group. In some instances, a water-soluble conjugated polymer is produced by inclusion of a water soluble group in a monomeric unit during polymer synthesis. In certain instances, a water soluble group is included via derivatization of a CP after polymer synthesis. For example, a water soluble group may be added via derivatization of a 6′-bromohexyl substituted CP.

The Signaling Chromophore

Chromophores useful in the inventions described herein include any substance which can absorb energy from a light harvesting multichromophore, when it is configured in energy-receiving proximity to the multichromophore and emit light. Chemical methods for attaching (e.g., directly or indirectly) a signaling chromophore to a sensor molecule and/or another assay component, such as a light harvesting multichromophore, are known.

The chromophore may be a lumophore or a fluorophore. Fluorophores of interest include, but are not limited to, fluorescent dyes, semiconductor nanocrystals, lanthanide chelates, and green fluorescent protein. Exemplary fluorescent dyes include, but are not limited to, fluorescein, 6-FAM, rhodamine, Texas Red, tetramethylrhodamine, a carboxyrhodamine, carboxyrhodamine 6G, carboxyrhodol, carboxyrhodamine 110, Cascade Blue, Cascade Yellow, coumarin, Cy2®, Cy3®, Cy3.5®, Cy5®, Cy5.5®, Cy-Chrome, phycoerythrin, PerCP (peridinin chlorophyll-a Protein), PerCP-Cy5.5, JOE (6-carboxy-4′,5′-dichloro-2′,7′-dimethoxyfluorescein), NED, ROX (5-(and-6)-carboxy-X-rhodamine), HEX, Lucifer Yellow, Marina Blue, Oregon Green 488, Oregon Green 500, Oregon Green 514, Alexa Fluor® 350, Alexa Fluor® 430, Alexa Fluor® 488, Alexa Fluor® 532, Alexa Fluor® 546, Alexa Fluor® 568, Alexa Fluor® 594, Alexa Fluor® 633, Alexa Fluor® 647, Alexa Fluor® 660, Alexa Fluor® 680, 7-amino-4-methylcoumarin-3-acetic acid, BODIPY® FL, BODIPY® FL-Br₂, BODIPY® 530/550, BODIPY® 558/568, BODIPY® 564/570, BODIPY® 576/589, BODIPY® 581/591, BODIPY® 630/650, BODIPY® 650/665, BODIPY® R6G, BODIPY® TMR, BODIPY® TR, conjugates thereof, and combinations thereof. Exemplary lanthanide chelates include europium chelates, terbium chelates and samarium chelates.

A wide variety of fluorescent semiconductor nanocrystals (“SCNCs”) are known in the art and may find use as a signalling chromophore; methods of producing and utilizing semiconductor nanocrystals are described in: PCT Publ. No. WO 99/26299 published May 27, 1999, inventors Bawendi et al; U.S. Pat. No. 5,990,479 issued Nov. 23, 1999 to Weiss et al., and Bruchez et al., Science 281:2013, 1998. Semiconductor nanocrystals can be obtained with very narrow emission bands with well-defined peak emission wavelengths, allowing for a large number of different SCNCs to be used as signaling chromophores in the same assay, optionally in combination with other non-SCNC types of signaling chromophores. In some cases, the signaling chromophore is a polynucleotide-specific dye such as an intercalating dye. Other dyes and fluorophores of interest are described at www.probes.com (Molecular Probes, Inc.).

In some cases, the signaling chromophore is a fluorescent protein, such as a green fluorescent protein (GFP). The term “green fluorescent protein” refers to both native Aequorea green fluorescent protein and mutated versions that have been identified as exhibiting altered fluorescence characteristics, including altered excitation and emission maxima, as well as excitation and emission spectra of different shapes (Delagrave, S. et al. (1995) Bio/Technology 13:151-154; Heim, R. et al. (1994) Proc. Natl. Acad. Sci. USA 91:12501-12504; Heim, R. et al. (1995) Nature 373:663-664). Delgrave et al. isolated mutants of cloned Aequorea victoria GFP that had red-shifted excitation spectra. Bio/Technology 13:151-154 (1995). Heim, R. et al. reported a mutant (Tyr66 to His) having a blue fluorescence (Proc. Natl. Acad. Sci. (1994) USA 91:12501-12504).

For multiplexed assays, a plurality of different signaling chromophores can be used with detectably different emission spectra. In some embodiments, a second signaling chromophore may be directly or indirectly attached to another of the assay components and/or to a substrate. In certain instances, the second signaling chromophore is used to receive energy from the initial signaling chromophore. In certain instances, this configuration can provide for significant additional selectivity. Energy can then be transferred from the excited light harvesting multichromophore to the initial signaling chromophore, which subsequently transfers energy to the second signaling chromophore, in an overall format that provides for detection of the target. This cascade of signaling chromophores can, in principle, be extended to use any number of signaling chromophores with compatible absorption and emission profiles.

Sensor Molecules

In some instances, a sensor molecule is provided that is complementary to the target to be detected. Any convenient sensor molecules that are complementary to a target may be utilized in the subject compositions and methods. Sensor molecules of interest include biomolecules, including but not limited to, a peptide or protein, a polynucleotide such as DNA or RNA, and an antibody. In certain embodiments, the sensor biomolecule is an antibody. In some cases, the sensor molecule is attached to a signaling chromophore. A variety of chemical methods for attaching a signaling chromophore to sensor are known in the art. Specific sensor structures, including structures conjugated to chromophores, can be custom-made using commercial sources or chemically synthesized.

In some embodiments, the sensor molecule is a sensor PNA that is complementary to a target polynucleotide to be assayed, and has a predetermined sequence. In certain embodiments, the sensor PNA can be branched, multimeric or circular, but is in some cases linear, and can contain nonnatural bases. The molecular structures of PNAs are well known. PNAs can be prepared with any desired sequence of bases. Chemical methods for attaching the signaling chromophore to the sensor PNA are well known. Specific sensor PNA structures, including structures conjugated to chromophores, can be custom-made using commercial sources or chemically synthesized.

In some instances, the sensor molecule is a sensor polynucleotide that is complementary to a target polynucleotide to be assayed, and has a predetermined sequence. The sensor polynucleotide can be branched, multimeric or circular, but is in some cases linear, and can contain nonnatural bases. The sensor polynucleotide can be prepared with any desired sequence of bases. Chemical methods for attaching the signaling chromophore to the sensor polynucleotide are known in the art. Specific sensor polynucleotide structures, including structures conjugated to chromophores, can be custom-made using commercial sources or chemically synthesized.

In some cases, the sensor molecule is a peptide or protein, e.g., a target binding protein. Any protein sensor molecule which can specifically bind to a target polynucleotide of interest can be employed in the compositions and methods disclosed. In some embodiments, the target binding protein is an antibody that specifically binds a target biomolecule. In certain embodiments, the target binding protein is a sensor polynucleotide binding protein (PBP) that specifically binds to a target polynucleotide to be assayed.

Protein biomolecules that find use as a sensor molecule for specifically binding a target biomolecule in the subject compositions and methods may be prepared using any convenient methods. In some cases, the protein sensor molecule is synthesized by the solid phase method and/or can be purified by HPLC and/or characterized by MALDI-TOF mass spectrum and amino acid analysis. The chemical methods for attaching a signaling chromophore to a protein sensor molecule are known. A specific example is the labelling composition including Tat-C*with fluorescein at the N-terminus.

Non-limiting examples of target binding proteins include, but are not limited to, transcription factors, splicing factors, poly(A) binding proteins, chromatin components, viral proteins, proteins which detect viral infection, replication factors, and proteins involved in mitotic and/or meiotic cell division. Examples of specific sensor proteins which can be used include Tat which binds to the Rev Responsive Element of human immunodeficiency virus (HIV), the matrix protein M1 which binds to Type A influenza virus RNA, and hnRNP U protein which binds to pre-ribosomal RNA.

Compositions

Aspects of the invention include compositions for detecting a target that include a signaling chromophore configured in energy-receiving proximity to a light harvesting multichromophore, such that amplification of the emission from the signaling chromophore occurs. The subject compositions include light harvesting multichromophores that are configured so that they can interact with a signaling chromophore which is in energy-receiving proximity therewith by virtue of any convenient connection. In some embodiments, the connection is an indirect connection via a sensor molecule. In some instances, the subject composition is utilized as a detection reagent in an assay to directly label a target biomolecule.

The proximity between a signaling chromophore and a light harvesting and luminescent multi-chromophore system may be ensured by any convenient connection. Terms such as “connected,” “attached,” “linked” and conjugated are used interchangeably herein and encompass direct as well as indirect connection, attachment, linkage or conjugation unless the context clearly dictates otherwise. Any convenient connection, attachment, linkage or conjugation of the signaling chromophore in energy-receiving proximity to the light harvesting multichromophore may provide for optical amplification via Förster energy transfer. The signaling chromophore may be connected directly or indirectly to the light harvesting multichromophore. In some embodiments, the signaling chromophore and the light harvesting multichromophore may be connected in a detection reagent prior to assaying a sample for the presence of a target.

In some cases, the connection between the light harvesting multichromophore and the signaling chromophore is indirect, e.g., is achieved by virtue of a binding event. In certain instances, the connection between the light harvesting multichromophore and the signaling chromophore is direct, e.g., via covalent bonds. In some instances, the connection between the light harvesting multichromophore and the signaling chromophore is direct and is achieved by virtue of a direct linkage or conjugation. In certain embodiments, the light harvesting multichromophore and the signaling chromophore may be attached to a sensor molecule.

Aspects of the invention include labelling compositions that include a signaling chromophore and a light harvesting multichromophore. As used herein, the terms “labelling composition” and “detection reagent” are used interchangeably, and refer to a composition that finds use in labelling and detecting a target analyte. When the average distance between the light harvesting multichromophore and the signaling chromophore is too large for effective energy transfer, there is little or no emission from the signaling chromophore. As such, the light harvesting multichromophore may be configured upon excitation to transfer energy to, and amplify the emission from, an acceptor signaling chromophore in energy-receiving proximity therewith.

It is understood that any convenient components and methods may be utilized in connecting the light harvesting multichromophore and the signaling chromophore to provide a labelling composition, as long as those components and methods permit energy transfer from the light harvesting multichromophore to the signaling chromophore in the labelling composition, for example via the Förster energy transfer mechanism. In some cases, the connection between the light harvesting multichromophore and the signaling chromophore is achieved where a signaling chromophore is conjugated to a sensor molecule that is also associated with a light harvesting multichromophore, where the sensor molecule has affinity for the target analyte. Under these circumstances, the connection between the signaling chromophore and the light harvesting multichromophore system is achieved, leading to efficient energy transfer and intense emission from the signaling chromophore. As such, it is understood that the signaling chromophore should be in energy-receiving proximity with the light harvesting multichromophore to achieve optical amplification in the labelling composition. Such energy-receiving proximity may be achieved by virtue of any convenient direct or indirect connection. It is understood that the target analyte may be labelled with the light harvesting multichromophore and an acceptor signaling chromophore in energy-receiving proximity therewith.

The subject compositions including a signaling chromophore and a light harvesting multichromophore may further include one or more components. In some cases, the composition includes a signaling chromophore, a light harvesting multichromophore and a sensor molecule that specifically binds a target.

In some instances, the invention provides a predominantly aqueous solution including a light harvesting multichromophore, a sensor molecule and a signaling chromophore. In certain embodiments, the sensor molecule is conjugated to the signaling chromophore. In certain cases, the sensor molecule is conjugated to the light harvesting multichromophore. In certain cases, the signaling chromophore is conjugated to the light harvesting multichromophore. In certain embodiments, the light harvesting multichromophore is conjugated to the signaling chromophore and the sensor molecule.

In some embodiments, the invention provides a predominantly aqueous solution comprising a light harvesting multichromophore (e.g., a CP), a “sensor biomolecule” and a signaling chromophore. In certain embodiments, the light harvesting multichromophore is conjugated to the signaling chromophore and the sensor molecule.

As discussed herein, the optical amplification provided by a water soluble light harvesting multichromophore can be used to detect a target analyte. In some cases, the amplification can be enhanced by using higher molecular weight water soluble conjugated polymers or other structures as the light harvesting multichromophore. The invention can be provided in a homogeneous format that utilizes the ease of fluorescence detection methods. Amplification of the emission from the acceptor signaling chromophore may occur when incident light is at a wavelength absorbed by the donor light harvesting multichromophore system as compared to when the acceptor signaling chromophore is directly excited by incident light, e.g., at the absorbance maximum of the acceptor. In certain embodiments, the amplification of the emission from the acceptor signaling chromophore is 2-fold greater or more, such as 3-fold greater or more, 4-fold greater or more, 6-fold greater or more, 8-fold greater or more, 10-fold greater or more, 15-fold greater or more, 25-fold greater or more, 30-fold greater or more, or even more as compared to when the acceptor signaling chromophore is directly excited by incident light.

In some embodiments of the compositions and methods, the ratio of the donor light harvesting multichromophore to the acceptor signaling chromophore is 1:1. In certain instances, the donor light harvesting multichromophore includes a conjugated polymer of aromatic repeat units and the ratio of the number of repeat units to the acceptor signaling chromophore is 100:1 or more.

Methods of Use

Aspects of the invention include contacting a sample with a predominantly aqueous composition including: (a) a light harvesting, luminescent multichromophore system such as, for example, a conjugated polymer, semiconductor quantum dot or dendritic structure that is water soluble; and (b) a sensor molecule conjugated to a luminescent signaling chromophore C*. The emission of a wavelength of light characteristic of the signaling chromophore-C* upon excitation of the light harvesting multichromophore may be used to detect the target. In some embodiments, the emission of the signaling chromophore is used to detect the sensor molecule-target complex.

The light harvesting multichromophores may be used in methods which screen the light harvesting multichromophores for any property of interest. For example, the light harvesting multichromophores may be tested for energy transfer to a chromophore, for increased fluorescent efficiency, for decreased self-quenching, for absorbance wavelength, and/or for emission wavelength.

A sensor molecule that is specific for the target may be used in conjugation with the light harvesting multichromophores, as can a signaling chromophore to which energy may be transferred from the light harvesting multichromophores. In certain instances, a sensor molecule of known structure is used to label the target in the sample. The sensor molecule may provide a signal specific to its complementary target in any of various ways, e.g., through incorporation of a specific signaling chromophore which can receive energy from the light harvesting multichromophore (e.g. CP). The signaling chromophore may be incorporated into the sensor molecule, or in some cases, may be recruited to a complex formed from the sensor molecule and the target. Formation of such a complex results in an increase of energy transfer from a light harvesting multichromophore upon excitation to the signaling chromophore, which may be detected directly or indirectly to provide information regarding the target.

The compositions described herein are useful for any assay in which a sample can be interrogated regarding a target biomolecule. In some embodiments, the assays involve determining the presence of the target in the sample or its relative amount, or the assays may be quantitative or semi-quantitative. As such, provided are methods of determining whether a target in present in a sample. In some embodiments, the method includes: contacting the sample with: a labelling composition (e.g., as described herein) to produce a labelling composition contacted sample; and assaying the labelling composition contacted sample for the presence of fluorescently labeled target analyte to evaluate whether the target analyte is present in the sample. Also provided are methods of detecting a target in a sample. In some instances, the method includes: contacting the sample with a labelling composition (e.g., as described herein) to produce a labelled target; and detecting the labelled target. The methods of the invention can all be performed in multiplex formats. A plurality of different sensor biomolecules can be used to detect corresponding different target biomolecules in a sample through the use of different signaling chromophores conjugated to the respective sensor biomolecules. In some cases, the light harvesting multichromophore (e.g., as described herein) is connected to the sensor biomolecule to provide for amplification of the signaling chromophore. Multiplex methods are provided employing 2, 3, 4, 5, 10, 15, 20, 25, 50, 100, 200, 400 or more different sensor biomolecules which can be used simultaneously to assay for corresponding different target biomolecules. The subject methods and compositions can be performed or utilized on a substrate, as well as in solution.

Any target molecule and any sensor molecule that can bind to each other can in principle be used in conjunction with the subject methods, where the light harvesting multichromophore may be associated with the sensor molecule. In some cases, this attachment may be accomplished through any convenient means to configure the light harvesting multichromophore in signaling juxtaposition with the signaling chromophore. In certain instances, the light harvesting multichromophore is attached to the sensor molecule in signaling juxtaposition to the signaling chromophore, where the sensor molecule specifically binds the target.

Targets

The target molecule may be a biomolecule, for example a peptide or protein, a polynucleotide such as DNA or RNA, and an antibody. Similarly, sensor molecules of interest include biomolecules. Exemplary sensor biomolecules of interest include, but are not limited to, a polynucleotide, a peptide nucleic acid (PNA), an antibody, a peptide or a protein.

Samples

Where the target is present in a biological sample, the portion of the sample comprising or suspected of comprising the target can be any source of biological material that can be obtained from a living organism directly or indirectly, including cells, tissue or fluid, and the deposits left by that organism, including viruses, mycoplasma, and fossils. The sample may comprise a target prepared through synthetic means, in whole or in part. Typically, the sample is obtained as or dispersed in a predominantly aqueous medium. Nonlimiting examples of the sample include blood, urine, semen, milk, sputum, mucus, a buccal swab, a vaginal swab, a rectal swab, an aspirate, a needle biopsy, a section of tissue obtained for example by surgery or autopsy, plasma, serum, spinal fluid, lymph fluid, the external secretions of the skin, respiratory, intestinal, and genitourinary tracts, tears, saliva, tumors, organs, samples of in vitro cell culture constituents (including but not limited to conditioned medium resulting from the growth of cells in cell culture medium, putatively virally infected cells, recombinant cells, and cell components), and a recombinant library comprising polynucleotide sequences.

The sample can be a positive control sample which is known to contain the target or a surrogate therefor. A negative control sample can also be used which, although not expected to contain the target, is suspected of containing it (via contamination of one or more of the reagents) or another component capable of producing a false positive, and is tested in order to confirm the lack of contamination by the target of the reagents used in a given assay, as well as to determine whether a given set of assay conditions produces false positives (a positive signal even in the absence of target in the sample).

The sample can be diluted, dissolved, suspended, extracted or otherwise treated to solubilize and/or purify any target present or to render it accessible to reagents, e.g., to detection reagents. Where the sample contains cells, the cells can be lysed or permeabilized to release the target within the cells.

Substrates

The methods described herein can be performed on a substrate in any of a variety of formats. One or more of the assay components may be incorporated in, attached to, or otherwise associated with the substrate, directly or indirectly. The substrate can comprise a wide range of materials, such as biological, nonbiological, organic, inorganic, or a combination of any of these.

Excitation and Detection of the Chromophores

Any convenient instrument that provides a wavelength that can excite the light harvesting multichromophore and is shorter than the emission wavelength(s) to be detected can be used for excitation. The excitation source in some cases does not significantly excite the signaling chromophore directly. The source may be: a broadband UV light source such as a deuterium lamp with an appropriate filter, the output of a white light source such as a xenon lamp or a deuterium lamp after passing through a monochromator to extract out the desired wavelengths, a continuous wave (cw) gas laser, a solid state diode laser, or any of the pulsed lasers. The emitted light from the signaling chromophore can be detected through any convenient device or technique. For example, a fluorimeter or spectrophotometer may be used to detect whether the test sample emits light of a wavelength characteristic of the signaling chromophore upon excitation of the multichromophore.

Kits

Kits comprising reagents useful for performing the methods of the invention are also provided. In one embodiment, a kit comprises a sensor molecule (e.g., as described herein) that specifically binds to a target molecule of interest and a light harvesting multichromophore (e.g., as described herein). The sensor molecule may be conjugated to a signaling chromophore. In certain instances, the sensor molecule is a protein. In certain embodiments, the light harvesting multichromophore is a conjugated polymer (CP).

The signaling chromophore may be configured in energy receiving proximity to the light harvesting multichromophore. In the presence of the target in the sample, the sensor molecule binds to the target which can be detected. The fluorescence detected includes increased emission of energy from the signaling chromophore.

The components of the kit can be retained by a housing. Instructions for using the kit to perform a method of the invention can be provided with the housing, and can be provided in any fixed medium. The instructions may be located inside the housing or outside the housing, and may be printed on the interior or exterior of any surface forming the housing which renders the instructions legible. The kit may be in multiplex form, containing pluralities of one or more different sensor molecules (e.g., PNAs) which can bind (e.g., hybridize) to corresponding different target molecules (e.g., target polynucleotides).

EXAMPLES

The following examples are set forth so as to provide those of ordinary skill in the art with a complete description of how to make and use the present invention, and are not intended to limit the scope of what is regarded as the invention. Efforts have been made to ensure accuracy with respect to numbers used (e.g., amounts, temperature, etc.) but some experimental error and deviation should be accounted for. Unless otherwise indicated, parts are parts by weight, temperature is degree centigrade and pressure is at or near atmospheric, and all materials are commercially available.

Example 1: PNA Sensor Molecules Example 1-1: Identification of a Multichromophore/Signaling Chromophore Pair for FRET

The ability to transfer energy from the light harvesting multichromophore system to the signaling chromophore on a sensor PNA was demonstrated using the water soluble conjugated polymer poly((9,9-bis(6′-N,N,N-trimethylammonium)-hexyl)-fluorene phenylene), polymer 1 with iodide counteranions, and the sensor peptide nucleic acid PNA-C* having the sequence 5′-CAGTCCAGTGATACG-3′ and conjugated to fluorescein (C*) at the 5′ position. Excitation was performed at 380 and 480 nm for 1 and PNA-C*, respectively. The data show that there is an optical window for the specific excitation of polymer 1. Moreover, there is excellent overlap between the emission of polymer 1 and the absorption of C* to allow FRET.

Example 1-2: Demonstration of Amplified Fluorescence Via FRET Between Light Harvesting Multichromophore and Signalling Chromophore in Complex with Target

The PNA-C* probe ([PNA-C*]=2.5×10⁻⁸ M) was contacted with an equimolar amount of the complementary 15 base pair ssDNA, (5′-CGTATCACTGGACTG-3′) (SEQ ID NO:), and in an identical fashion with a non-complementary 15 base ssDNA, (5′-ACTGACGATAGACTG-3′) (SEQ ID NO:), in separate vessels in the absence of polymer 1. The annealing step was performed in the absence of buffer, i.e. at low ionic strength, at 2° C. below the T_(m) of PNA-C* (72° C. at 10⁻⁸M, pH=5.5). A melting experiment was performed and the absorbance monitored by UV/Vis spectroscopy at 260 nm. Increasing the temperature led to an increase in absorbance upon melting of the hybridized duplex in the sample containing the complementary ssDNA, as the two single strands absorb more highly than the hybridized duplex. As expected, the sample containing the non-complementary ssDNA did not show such an increase in absorbance, as no duplex was formed in that sample.

FRET was measured in annealed samples containing the complementary and non-complementary ssDNAs and polymer 1 ([1]=2.3×10⁻⁷M). The normalized emission spectra of PNA-C* in the presence of complementary and non-complementary DNA upon excitation of polymer 1 are shown in FIG. 1. A FRET ratio>11 times higher for the PNA/DNA hybrid was detected, relative to the non-complementary pair. The fluorescein emission was more than 8 times larger than that obtained from direct C* excitation in the absence of 1. This increased C* emission in the energy transfer complex indicates that optical amplification is provided by the multichromophore (polymer 1).

Example 2: Polynucleotide Sensor Molecules Example 2-1: Identification of FRET Between Light Harvesting Multichromophore and Signalling Chromophore

Energy transfer from the light harvesting multi-chromophore system to the signaling chromophore was demonstrated using the water soluble conjugated polymer poly(9,9-bis(6′-N,N,N-trimethylammonium)-hexyl)-fluorene phenylene), polymer 1 with iodide counteranions. The sensor polynucleotide sequence was 5′-GTAAATGGTGTTAGGGTTGC-3′ (SEQ ID NO:), corresponding to the anthrax (Bacillus anthracis) spore encapsulation plasmid, pX02, with fluorescein at the 5′ position, forming an example of oligo-C*. The data shows an optical window for the excitation of polymer 1, between the absorption of DNA and fluorescein. Direct excitation of polymer 1 results in energy transfer (ET) to fluorescein. The absorbance overlap of fluorescein with the emission of polymer 1 was selected to ensure FRET. The extent of ET is evaluated by the ratio of integrated acceptor to donor emission.

Example 2-2: Demonstration of Amplified Fluorescence Via FRET Between Light Harvesting Multichromophore and Signalling Chromophore in a Complex with a Target

The sensor polynucleotide ([Oligo-C*]=2.1×10⁻⁸M) was annealed at 2° C. below its T_(m) (58.4° C.) in the presence of an equal molar amount of a 40 base pair strand containing a complementary 20 base pair sequence, 5′-CATCTGTAAATCCAAGAGTAGCAACCCTAACACCATTTAC-3′ (SEQ ID NO:), and in an identical fashion with a non-complementary 40 base strand with the sequence 5′-AAAATATTGTGTATCAAAATGTAAATGGTGTTAGGGTTGC-3′ (SEQ ID NO:). Direct comparison of the resulting fluorescence reveals an ET ratio greater than 6 fold higher for the hybridized DNA. Using a Xenon lamp fluorometer, equipped with a standard PMT, the hybridized DNA provided over 3 fold greater ET ratios, at [sensor polynucleotide]=2.8×10⁻⁹M, than did the non-hybridized DNA.

Example 2-3: FRET Transfer to a Target Specific Dye

Experiments using 1 and ethidium bromide (“EB”) as a signaling chromophore demonstrate that direct energy transfer from 1 to EB could be shown in the presence of double-stranded DNA. The sensor polynucleotide (5′-ATCTTGACTATGTGGGTGCT-3′) (SEQ ID NO:) lacking the signaling chromophore ([Oligo]=1×10⁻⁸ M) was annealed at 2° C. below its T_(m) (58.5° C.) in the presence of an equal molar amount of a 20 base pair strand containing a complementary 20 base pair sequence, (5′-AGCACCCACATAGTCAAGAT-3′) (SEQ ID NO:), and in an identical fashion with a non-complementary 20 base pair strand with the sequence (5′-CGTATCACTGGACTGATTGG-3′) (SEQ ID NO:). The two DNA mixtures were mixed with Ethidium Bromide ([EB]=1.1×10⁻⁶ M) at room temperature in potassium phosphate monobasic-sodium hydroxide buffer solution (50 mM, pH=7.40) where the intercalation of the EB occurred within the duplex structure of the hybridized DNA pair. Addition of polymer 1 in water ([1]=1.6×10⁻⁷M) and subsequent excitation of 1 (380 nm) resulted in energy transfer from 1 to the intercalated EB only in the case of hybridized or double stranded DNA.

Example 3: Protein Sensor Molecules

The TAR RNA and dTAR RNA oligonucleotides described below were purchased from Dharmacon Research Inc. (Lafayette, USA). The polypeptides modified by fluorescein on the N-terminus (Tat-C* and SH3-C*) were custom-made by Sigma-Genosys (Texas, USA). All the fluorescence and FRET experiments were carried out using a PTI Quantum Master fluorometer equipped with a Xenon lamp excitation source in tris-EDTA buffer solution (10 mM, pH=7.4).

Example 3-1

Emission spectra and absorption spectra were obtained to show that there is excellent overlap between the emission of polymer 1 and the absorption of Tat-C* to ensure fluorescence resonance energy transfer.

Example 3-2

Emission spectra and absorption spectra were obtained to show that there is excellent overlap between the emission of oligomer 1 and the absorption of Tat-C* to ensure fluorescence resonance energy transfer.

Example 3-3

Emission spectra and absorption spectra were obtained to show that there is excellent overlap between the emission of oligomer 2 and the absorption of Tat-C* to ensure fluorescence resonance energy transfer.

Example 3-4

The Tat-C* probe ([Tat-C*]=1.0×10⁻⁸ M) was mixed with an equimolar amount of the TAR RNA at room temperature, and in an identical fashion with a non-specific dTAR RNA. It is known that a bulge structure in TAR RNA is a requirement for Tat peptide binding to TAR RNA. dTAR RNA is closely related in structure to TAR RNA, lacking the three base bulge structure necessary for Tat binding.

Addition of oligomer 1 in water ([oligomer 1]=8.0×10⁻⁸ M) and subsequent comparison of the resulting fluorescence of Tat-C* obtained by excitation at 365 nm reveals an intensity ratio>10 times higher for the Tat-C*/TAR RNA, relative to the non-specific Tat-C*/dTAR RNA pair. The fluorescein emission is more than 25 times larger than that obtained from direct Tat-C* excitation at the absorption maximum of fluorescein in the absence of oligomer 1. The increased Tat-C* emission in the energy transfer complex indicates that optical amplification is provided by the conjugated oligomer 1.

Example 3-5

The Tat-C* probe ([Tat-C*]=1.0×10⁻⁸M) was mixed with an equimolar amount of the TAR RNA at room temperature, and in an identical fashion with a non-specific dTAR RNA. Addition of oligomer 2 in water ([oligomer 2]=6.0×10⁻⁸ M) and subsequent comparison of the resulting fluorescence of Tat-C* obtained by excitation at 375 nm reveals an intensity ratio 15 times higher for the Tat-C*/TAR RNA, relative to the non-specific Tat-C*/dTAR RNA pair. The fluorescein emission is more than 30 times larger than that obtained from direct Tat-C* excitation in the absence of oligomer 2. The increased Tat-C* emission in the energy transfer complex indicates that optical amplification is provided by the conjugated oligomer 2.

Example 3-6

The water soluble conjugated polymer 1 (average n=app. 15) was utilized as the light harvesting chromophore. The Tat-C* probe ([Tat-C*]=1.0×10⁻⁸M) was mixed with an equimolar amount of the TAR RNA at room temperature, and in an identical fashion with a non-specific dTAR RNA. Addition of polymer 1 in water ([polymer 1]=4.8×10⁻⁷M) into the mixture of Tat-C* and TAR RNA results in fluorescence of Tat-C* with an intensity ratio>15 times higher than that of the non-specific Tat-C*/dTAR RNA and 10 times larger than that obtained from direct Tat-C* excitation in the absence of polymer 1. Thus, significantly higher FRET ratios and correspondingly higher sensitivities can be achieved.

Example 3-7

Another peptide sequence labeled with fluorescein at the N-terminus (SH3-C*, AKPRPPRPLPVAC in single letter code) (SEQ ID NO:) which cannot specifically bind to TAR RNA was also utilized as the signal molecule. The mixture of [SH3-C* or Tat-C*]=1.0×10⁻⁸ M, [TAR RNA]=1.0×10⁻⁸M and [oligomer 1]=8.0×10⁻⁸M) shows C* emission only when the Tat-C* was present.

Example 4

Conjugated polymers were synthesized through the Suzuki coupling reaction and a post-polymerization quarternization step. Synthetic examples are given with respect to the specific polymers under Formula 1. The synthetic routes are shown in the Schemes below

An overview of the methods depicted in Schemes 1-4 is as follows. 1,3-Bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan)phenylene (1) was obtained in 46% yield by treating 1,3-diiodobenzene with bis(pinacolato)diborane in the presence of PdCl₂(dppf) and potassium acetate in DMSO. 2,7-Dibromo-9,9-bis(6′-bromohexyl)fluorene (2) was obtained by the treatment of 2,7-dibromofluorene with 50% KOH, followed by addition of excess of 1,6-dibromohexane in 85% yield. Coupling of one equivalent of the dibromide monomer with one net equivalent of diboronic acid or diboronic ester, under Suzuki coupling conditions using PdCl₂(dppf) in refluxing THF/H₂O for 24 h, followed by purification gave the desired polymers including bromo-substituted alkyl substituents in 39% to 88% yield. The products were thoroughly washed with methanol and acetone, and then dried in vacuum for 24 h. Formation of the trimethylamine derivatized polymers was achieved by stirring the polymers in condensed trimethylamine in a THF/H₂O solvent mixture for 24 h.

Example 4-1: 1,3-Bis(4,4,5,5,-tetramethyl-1,3,2-dioxaborolan)phenylene (1)

A flask charged with 1,3-diiodobenzene (1.0 g, 3 mmol), bis(pinacolato)diborane (2.3 g, 9 mmol), potassium acetate (2.1 g, 21 mmol), PdCl₂(dppf) (150 mg, 0.18 mmol), and 15 mL of anhydrous DMSO was degassed for 15 minutes. The mixture was stirred at 80° C. for 12 h, cooled to room temperature and then poured into 100 mL of ice water. The mixture was extracted with CHCl₃, and the combined organic layers were dried over anhydrous MgSO₄. After the solvent was evaporated, the residue was purified by chromatography using silica gel (Hexane:CHCl3=1:1) and then recrystallized from ethanol to afford 1 (460 mg, 46%) as a white solid. ¹H NMR (200 MHz, CDCl3): δ 8.28 (s, 1H), 7.91-7.89 (d, 2H), 7.38 (t, 1H), 1.35 (s, 24H). ¹³C NMR (50 MHz, CDCl₃): δ 141.4, 137.8, 127.3, 83.9, 25.1.

Example 4-2: 2,7-Dibromo-9,9-bis(6′-bromohexyl)fluorene (2)

To a mixture of tetrabutylammonium bromide (300 mg, 9.3 mmol), aqueous potassium hydroxide (100 mL, 50%) and 1,6-dibromohexane (22.6 g, 92.6 mmol) was added 2,7-dibromofluorene at 75° C. After 15 minutes, the mixture was cooled down to room temperature, and extracted with CH₂Cl₂. The organic layer was washed with water, aqueous HCl, water and brine, dried over MgSO₄, and then concentrated. Unreacted 1,6-dibromohexane was distilled off. The residue was purified by silica gel column chromatography (Hexane:CHCl₃=9:1) and recrystallized from ethanol to give 2 (4.8 g, 80%) as a white solid. ¹H NMR (200 MHz, CDCl₃): δ 7.2-7.4 (m, 6H), 3.12 (t, 4H), 1.75 (t, 4H), 1.5 (m, 4H), 1.0 (m, 8H), 0.4 (m, 4H). ¹³C NMR (50 MHz, CDCl₃): δ 152.3, 139.2, 130.5, 126.2, 121.7, 121.4, 55.7, 40.2, 34.1, 32.8, 29.1, 27.9, 23.6.

Example 4-3: Poly(9,9-bis(6′-bromohexyl)fluorene-co-alt-1,3-phenylene) (M₁₀₀P₀)

2,7-Dibromo-9,9-bis(6′-bromohexyl)fluorene (325 mg, 0.5 mmol), 1,3-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan)phenylene (166 mg, 0.5 mmol), Pd(PPh3)4 (8 mg) and potassium carbonate (830 mg, 6 mmol) were placed in a 25 mL round bottle flask. A mixture of water (3 mL) and toluene (5 mL) was added to the flask. After degassing, the mixture was refluxed at 85° C. for 20 h, and then precipitated into methanol. The polymer was filtered and washed with methanol and acetone, and then dried in vacuum for 24 h to afford M₁₀₀P₀ (251 mg, 88%) as a light yellow solid. 1H NMR (200 MHz, CDCl₃): δ 7.9-7.6 (m, 10H), 3.3-3.2 (t, 4H), 2.1 (m, 4H), 1.7-1.6 (m, 4H), 1.3-1.2 (m, 8H), 0.8 (m, 4H). 13C NMR (50 MHz, CDCl₃): δ 152.1, 142.9, 140.9, 130.1, 129.5, 128.0, 126.8, 122.5, 120.9, 55.9, 40.9, 34.5, 33.3, 29.7, 28.5, 24.3. GPC (THF, polystyrene standard), Mw: 40,250 g/mol; Mn: 14,980 g/mol; PDI: 2.8. UV-vis (CHCl₃): λmax=337 nm; is PL (CHCl₃): λmax=363 nm.

Example 4-4: Poly(9,9-bis(6′-bromohexyl)fluorene-co-alt-1,4-phenylene) (M₀P₁₀₀)

2,7-Dibromo-9,9-bis(6′-bromohexyl)fluorene (325 mg, 0.5 mmol), 1,4-phenylenebisboronic acid (82.9 mg, 0.5 mmol), Pd(dppf)Cl₂ (7 mg) and potassium carbonate (830 mg, 6 mmol) were placed in a 25 mL round bottle flask. A mixture of water (3 mL) and THF (6 mL) was added to the flask and degassed. The mixture was refluxed at 85° C. for 24 h, and then precipitated into methanol. The polymer was filtered and washed with methanol and acetone, and then dried in vacuum for 24 h to afford M0P100 (220 mg, 78%) as an off-white solid. ¹H NMR (200 MHz, CDCl3): δ 7.8 (m, 5H), 7.7-7.6 (m, 4H), 7.5 (m, 1H), 3.3 (t, 4H), 2.1 (m, 4H), 1.7 (m, 4H), 1.3-1.2 (m, 8H), 0.8 (m, 4H). 13C NMR (50 MHz, CDCl3): δ 151.9, 140.9, 140.7, 140.2, 128.1, 126.6, 121.8, 120.8, 55.7, 40.9, 34.5, 33.2, 29.6, 28.3, 24.2. GPC (THF, polystyrene standard), Mw: 25,850 g/mol; Mn: 12,840 g/mol; PDI: 2.0. UV-vis (CHCl3): λmax=372 nm; PL (CHCl3): λmax=408 nm.

Example 4-5: Random Copolymer M₂₅P₇₅

2,7-Dibromo-9,9-bis(6′-bromohexyl)fluorene (325 mg, 0.5 mmol), 1,4-phenylenebisboronic acid (62.2 mg, 0.375 mmol), 1,3-phenylenebisboronic acid (20.7 mg, 0.125 mmol), Pd(dppf)Cl2 (7 mg) and potassium carbonate (830 mg, 6 mmol) were placed in a 25 mL round bottle flask. A mixture of water (3 mL) and THF (6 mL) was added to the flask and degassed. The mixture was refluxed at 85° C. for 24 h, and then precipitated into methanol. The polymer was filtered and washed with methanol and acetone, and then dried in vacuum for 24 h to afford M₂₅P₇₅ (248 mg, 88%) as an off-white solid. ¹H NMR (200 MHz, CDCl₃): δ 7.9-7.6 (m, 10H), 3.3-3.2 (t, 4H), 2.1 (m, 4H), 1.7-1.6 (m, 4H), 1.3-1.2 (m, 8H), 0.8 (m, 4H). GPC (THF, polystyrene standard), Mw: 29,000 g/mol; Mn: 14,720 g/mol; PDI: 1.9. UV-vis (CHCl₃): λmax=365 nm; PL (CHCl₃): λmax=407 nm.

Example 4-6: Random Copolymer M₅₀P₅₀

2,7-Dibromo-9,9-bis(6′-bromohexyl)fluorene (325 mg, 0.5 mmol), 1,4-phenylenebisboronic acid (41.5 mg, 0.25 mmol), 1,3-phenylenebisboronic acid (41.5 mg, 0.25 mmol), Pd(dppf)Cl2 (7 mg) and potassium carbonate (830 mg, 6 mmol) were placed in a 25 mL round bottle flask. A mixture of water (3 mL) and THF (6 mL) was added to the flask and degassed. The mixture was refluxed at 85° C. for 24 h, and then precipitated into methanol. The polymer was filtered and washed with methanol and acetone, and then dried in vacuum for 24 h to afford M₅₀P₅₀ (220 mg, 78%) as an off-white solid. ¹H NMR (200 MHz, CDCl₃): δ 7.9-7.6 (m, 10H), 3.3-3.2 (t, 4H), 2.1 (m, 4H), 1.7-1.6 (m, 4H), 1.3-1.2 (m, 8H), 0.8 (m, 4H). GPC (THF, polystyrene standard), Mw: 17,340 g/mol; Mn: 10,080 g/mol; PDI: 1.7. UV-vis (CHCl₃): λmax=351 nm; PL (CHCl₃): λmax=405 nm.

Example 4-7: Random Copolymer M₇₅P₂₅

2,7-Dibromo-9,9-bis(6′-bromohexyl)fluorene (325 mg, 0.5 mmol), 1,4-phenylenebisboronic acid (20.7 mg, 0.125 mmol), 1,3-phenylenebisboronic acid (62.2 mg, 0.375 mmol), Pd(dppf)Cl₂ (7 mg) and potassium carbonate (830 mg, 6 mmol) were placed in a 25 mL round bottle flask. A mixture of water (3 mL) and THF (6 mL) was added to the flask. After degassing, the mixture was refluxed at 85° C. for 24 h, and then precipitated into methanol. The polymer was filtered and washed with methanol and acetone, and then dried in vacuum for 24 h to afford M₇₅P₂₅ (130 mg, 46%) as an off-white solid. ¹H NMR (200 MHz, CDCl₃): δ 7.9-7.6 (m, 10H), 3.3-3.2 (t, 4H), 2.1 (m, 4H), 1.7-1.6 (m, 4H), 1.3-1.2 (m, 8H), 0.8 (m, 4H). GPC (THF, polystyrene standard), Mw: 13,000 g/mol; Mn: 8,700 g/mol; PDI: 1.4. UV-vis (CHCl3): λmax=342 nm; PL (CHCl₃): λmax=400 nm.

Example 4-8: Random Copolymer M₉₀P₁₀

2,7-Dibromo-9,9-bis(6′-bromohexyl)fluorene (325 mg, 0.5 mmol), 1,4-phenylenebisboronic acid (8 mg, 0.05 mmol), 1,3-phenylenebisboronic acid (75 mg, 0.45 mmol), Pd(dppf)Cl₂ (7 mg) and potassium carbonate (830 mg, 6 mmol) were placed in a 25 mL round bottle flask. A mixture of water (3 mL) and THF (6 mL) was added to the flask and degassed. The mixture was refluxed at 85° C. for 24 h, and then precipitated into methanol. The polymer was filtered and washed with methanol and acetone and then dried in vacuum for 24 h to afford M₉₀P₁₀ (110 mg, 39%) as an off-white solid. ¹H NMR (200 MHz, CDCl₃): δ 7.9-7.6 (m, 10H), 3.3-3.2 (t, 4H), 2.1 (m, 4H), 1.7-1.6 (m, 4H), 1.3-1.2 (m, 8H), 0.8 (m, 4H). GPC (THF, polystyrene standard), Mw: 8,400 g/mol; Mn: 5,800 g/mol; PDI: 1.4. UV-vis (CHCl3): λmax=338 nm; PL (CHCl₃): λmax=400 nm.

Example 4-9: Derivatization of Conjugated Polymers

The following procedure may be adapted for use in the derivatization of a conjugated polymer that includes bromo substituted alkyl groups.

Condensed trimethylamine (2 mL) was added dropwise to a solution of the neutral polymer M₁₀₀P₀ (60 mg) in THF (10 mL) at −78° C. The mixture was allowed to warm up to room temperature. The precipitate was re-dissolved by the addition of water (10 mL). After the mixture was cooled down to −78° C., extra trimethylamine (2 mL) was added and the mixture was stirred for 24 h at room temperature. After removing most of the solvent, acetone was added to precipitate M₁₀₀P₀+(63 mg, 78%) as a light yellow powder. ¹H NMR (500 MHz, CD₃OD): δ 8.1-7.7 (m, 10H), 3.3-3.2 (t, 4H), 3.1 (s, 18H), 2.3 (br, 4H), 1.6 (br, 4H), 1.3 (br, 8H), 0.8 (br, 4H). ¹³C NMR (125 MHz, CD₃OD): δ 151.9, 142.4, 140.9, 140.6, 129.77, 126.5, 126.1, 125.6, 121.6, 120.5, 66.7, 55.7, 52.5, 40.1, 29.2, 25.8, 23.8, 22.6. UV-vis (H₂O): λmax=334 nm; PL (H₂O): λmax=369 nm. ε=3.69×10⁴ M⁻¹ cm⁻¹ per monomer unit.

Example 4-10

UV-vis and fluorescence spectra for a range of compositions are summarized in Table 3. There is a progressive blue shift in absorption with increasing meta content, consistent with the more effective electronic delocalization across para linkages. The ε values are lowest for polymers with intermediate compositions because the random distribution of conjugated segments results in broader absorption bands.

TABLE 3 Optical properties of polymers of interest. M_(n)P_(m) ⁺ λ_(max), abs λ_(max), em ε^(a) Φ_(buffer) ^(b) M₁₀₀P₀+ 335 369 37 0.51 M₉₀P₁₀+ 337 403 32 0.57 M₇₅P₂₅+ 347 410 30 0.50 M₅₀P₅₀+ 361 421 32 0.44 M₂₅P₇₅+ 376 417 42 0.42 M₀P₁₀₀+ 384 417 46 0.42 ^(a)unit: 10³ Lcm⁻¹ mol⁻¹ ^(b) 50 mmol phosphate buffer, quinine bisulfite as the standard

Fluorescence spectra in water as a function of polymer composition. Increasing the para content past the 50:50 ratio does not perturb the emission maxima. Fast energy transfer, either by intra- or interchain mechanisms, localizes excitations on the longest conjugation segments within the lifetime of the excited state. Table 3 shows that there is little variation in the fluorescence quantum yields (ϕ in Table 3).

Equation 1 describes how the FRET rate changes as a function of the donor-acceptor distance (r), the orientation factor (κ), and the overlap integral (J).

$\begin{matrix} {{k_{t{(r)}} \propto {\frac{1}{r^{6}} \cdot k^{2} \cdot {J(\lambda)}}}{{J(\lambda)} = {\underset{0}{\overset{\infty}{\mathcal{o}}}{F_{D}(\lambda)}{ɛ_{A}(\lambda)}\lambda^{4}d\;\lambda}}} & (1) \end{matrix}$

Since M₅₀P₅₀+ and M₀P₁₀₀+ have similar emission frequencies, the value of J using a common acceptor dye should be nearly identical between the two polymers. The fluorescence lifetimes of the two polymers are similar (400±50 ps). Therefore, differences in FRET efficiencies to a common acceptor chromophore can extract information relevant to the average polymer/acceptor chromophore distance and the orientation of transition moments.

Example 4-11

FIG. 2 shoes a comparison of the intensity of signaling chromophore (e.g., EB (EB=Ethidium bromide)) emission from various compositions where a conjugated polymer and a signaling chromophore are connected via a biomolecule, e.g., polymer/ds-DNA/EB in 50 mmol phosphate buffer (pH=7.4) with [ds-DNA]=1.0 E⁻⁸ M, [Polymer RU]=2.0 E⁻⁷ M, [EB]=1.1 E⁻⁶ M. Emission intensity was normalized relative to the E value at the excitation wavelength.

Although the invention has been described in some detail with reference to the preferred embodiments, those of skill in the art will realize, in light of the teachings herein, that certain changes and modifications can be made without departing from the spirit and scope of the invention. Accordingly, the invention is limited only by the claims. 

What is claimed is:
 1. A method comprising: (a) applying a light source to an aqueous solution comprising: a donor conjugated polymer having a delocalized electronic structure and configured upon excitation to transfer energy to, and amplify the emission from, an acceptor signaling chromophore; and the acceptor signaling chromophore that is a fluorescent dye in energy-receiving proximity to the donor conjugated polymer; and (b) detecting whether light is emitted from the signaling chromophore.
 2. The method according to claim 1, wherein the ratio of the donor conjugated polymer to the acceptor signaling chromophore is 1:1.
 3. The method according to claim 1, wherein the donor conjugated polymer comprises aromatic repeat units and the ratio of the number of aromatic repeat units to the acceptor signaling chromophore is 100:1 or more.
 4. The method according to claim 1, wherein amplification of the emission from the acceptor signaling chromophore occurs when incident light is at a wavelength absorbed by the donor conjugated polymer.
 5. The method according to claim 1, wherein the donor conjugated polymer is directly linked to the acceptor signaling chromophore.
 6. The method according to claim 1, wherein the donor conjugated polymer is neutral.
 7. The method according to claim 1, wherein the donor conjugated polymer is linked to a sensor biomolecule that specifically binds to a target.
 8. The method according to claim 7, wherein the sensor biomolecule is a target binding protein.
 9. The method according to claim 8, wherein the sensor biomolecule is an antibody.
 10. The method according to claim 1, wherein the donor conjugated polymer comprises a conjugated segment having the structure:

wherein: R¹, R², R³, R⁴ and R⁵ are independently selected from the group consisting of alkyl, alkenyl, alkoxy, alkynyl, and aryl, alkylaryl, arylalkyl, and polyalkylene oxide, each optionally substituted, which may contain one or more heteroatoms, or may be not present; A, B, C, D and I are independently selected from the group consisting of: hydrogen, —SiR′R″R′″, —N+R′R″R′″, a guanidinium group, histidine, a polyamine, a pyridinium group, and a sulfonium group; E is selected from the group consisting of not present, —O—, —S—, —C(O)—, —C(O)O—, —C(R)(R′)—, —N(R′)—, and —Si(R′)(R″), wherein R′ and R″ are independently selected from the group consisting of hydrogen, C₁₋₁₂ alkyl and C₁₋₁₂ alkoxy and C₃₋₁₀ cycloalkyl; and n is 1 to 10,000; wherein at least one of —R¹-A, —R²—B, —R³—C, —R⁴-D and —R⁵—I comprises a water soluble group (WSG).
 11. The method according to claim 10, wherein R³ and R⁴ are alkyl, each optionally substituted, which may contain one or more heteroatoms.
 12. The method according to claim 10, wherein E and R⁵ are not present.
 13. A method comprising: (a) applying a light source to an aqueous composition comprising a conjugated polymer having a delocalized electronic structure and comprising contributing chromophores configured upon excitation to transfer energy to acceptor signaling chromophores and acceptor signaling chromophores in energy-receiving proximity to the contributing chromophores; and (b) detecting whether light is emitted from the signaling chromophore.
 14. The method according to 13, wherein the contributing chromophores are fluorenes or substituted fluorenes.
 15. The method according to claim 14, wherein the signaling chromophores comprise a fluorophore.
 16. The method according to claim 15, wherein the fluorophore comprises a BODIPY.
 17. The method according to claim 15, wherein the donor conjugated polymer is linked to a sensor biomolecule that specifically binds to a target.
 18. The method according to claim 17, wherein the sensor biomolecule is a target binding protein.
 19. The method according to claim 18, wherein the sensor biomolecule is an antibody. 